1. Field of the Invention
The present invention relates to a method for controlling the discharge of fluids during a process for vulcanization and molding of a green tire and to a tire for vehicle wheels.
2. Description of the Related Art
A tire for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, the inner diameter of which substantially corresponds to the so-called “fitting diameter” of the tire on a respective mounting rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers disposed in radially superposed relationship with each other and with the carcass ply and provided with textile or metallic reinforcing cords having a crossed orientation and/or being substantially parallel to the circumferential extension direction of the tire. A tread band is applied at a radially external position to the belt structure, which tread band too is made of elastomeric material like other semifinished products constituting the tire. Respective sidewalls of elastomeric material are also applied at an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tires of the “tubeless type”, an airtight coating layer, usually referred to as “liner”, covers the inner surfaces of the tire.
After building of the green tire carried out by assembly of respective components, a vulcanization and molding treatment is generally accomplished aiming at determining the structural stabilization of the tire by cross-linking of the elastomeric compounds and at impressing the tire with the desired tread pattern as well as with possible distinctive graphic marks at the tire sidewalls.
Herein and in the following of the present specification, by low-section tire it is intended a tire having a reduced section ratio, i.e. in which the section height measured between the radially outermost point of the tread band and the radially innermost point of the bead is less than about 50% of the section width axially measured at the maximum-chord point of the tire. More specifically, in the present context low-section tires are considered in which the section height is included between about 20% and about 50% of the section width, preferably between about 30% and about 45% of the section width.
Document WO 2008/099236, in the name of the same Applicant, discloses a process in which the carcass ply is applied around an outer surface of a building drum. Application of first components of the carcass sleeve takes place at the building drum by means of auxiliary devices. These auxiliary devices comprise one or more dispensers supplying at least one continuous elongated element of elastomeric material while the building drum is being driven in rotation about its geometric axis so as to form the liner on the outer surface and the bearing surfaces. An annular anchoring structure defining the fitting diameter is coaxially engaged around each of the end flaps. An outer sleeve comprising at least one belt structure possibly associated with a tread band is disposed at a coaxially centered position around the carcass sleeve applied onto the building drum. Through axial approaching of two halves forming the building drum, the carcass sleeve is shaped into a toroidal configuration to cause application thereof against a radially internal surface of the outer sleeve.
Document US 2003/012284 discloses a pressing bladder for pressing an inner surface of a tire through use of a pressurized heating means during vulcanization of a green tire. The pressing bladder comprises a textile layer and rubber layers disposed upon each other. The pressing bladder is positioned inside the green tire enclosed in a mold. A high-temperature and high-pressure fluid is fed into the pressing bladder, causing expansion of same so that the tire is pushed against the inner wall of the mold. In this way, the outer face of the green tire is impressed with a tread pattern and the green tire is vulcanized by a heating action carried out by the heating fluid and the mold. If the textile layer consists of a knitted fabric and faces the tire, the residual gas interposed between the pressing bladder and the green tire spreads over the unevenness of the outer fabric surface and comes out of the tire end portions without forming big bubbles. If the knitted-fabric layer is at the inside and the rubber layer faces the tire, during pressing the uneven features of the fabric layer are transferred to the rubber layer on the mold side thus forming depressions and elevations. The residual gas spreads through the depressions and comes out of the end portions of the tire.